A study is proposed of the Lewis Acid and/or pressure promoted Diels-Alder reactions of 3-methyl-2H-thiopyran, I, its 4- and/or 6-trialkylsilyloxy derivatives and their 2H-pyran analogs with 2,6-dimethyl-p-quinone and 2-methoxy-6-methyl-p-quinone, II. The expected major adduct under these conditions is III. The reaction of I and II to give III will provide an entry into a novel and general strategy for the synthesis of the nagilactones, inumakilactones, hallactones and podolactones, members of a large group of diterpene dilactones possessing the basic structure IV. These naturally occurring compounds display important antitumor, antibiotic and insecticidal properties and contrasting plant growth regulatory activity. The most biologically active members, nagilactone F and antibiotic LL-Z1271Alpha, are targeted for total synthesis to demonstrate the validity of the strategy. An additional objective of this research is to investigate the effects of very high pressure (15Kbar) on potential cis-dienethione/cis-dienone reversible 2H-thiopyran/2H-pyran equilibria.